[sdiy] OT: Fixing RME Fireface 800 power supply

Gil W. gil_we at yahoo.com
Tue Jul 3 15:28:57 CEST 2012

I got a dead FF800 which I'd like to repair. I used the PS unit from a working FF800 and the dead unit came alive, so obviously the PS is dead. Off circuit, no output voltages from the PS are seen. No burnt out parts, no shorts of transistors/diodes/diode bridge, looks clean. I noticed that in the dead PS unit, there's no "click" sound heard as you power the unit on... On the working unit, you will head a click sound a second after turning it on, but I don't see any relay in the PS, the click comes from what appears to be a transformer. 

I took parts from the working PS unit and places instead the one in the dead unit to see if I can find the defective part (RME doesn't let the schematic become available...). This way, I replaced all large transistors, the photocoupler, the UC3842 ic, coil and transformer. I also ran over all solder joints just in case there's a crack. So far no change except when I replaced the UC3842 which made the transformer make a high pitched noise when powering on and off (no click - and the working PS doesn't make that noise).

Before I'm going to look for a new one, any suggestions of what can be check further ? Thanks very much !

Here's how it looks like:


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